Prostate cancer is the most commonly diagnosed cancer in American men. Transperineal interstitial permanent prostate brachytherapy (TIPPB) is a minimally invasive, low cost, curative treatment method used to treat prostate cancer. In this treatment, 90-150 radioactive seeds are implanted into the prostate to irradiate and kill the prostate along with the cancer. An ultrasound (US) probe is inserted into the rectum of a patient and operated to capture a series of trans-rectal ultrasound (TRUS) images of the prostate (hereinafter referred to as “captured images”) spaced at predetermined distances along the length of the prostate. Each captured image comprises a cross-section of the prostate. Typically, oncologists manually identify the contour of the prostate in each image to define a segmented volume of the prostate. The process of identifying the contour of the cross-section of a prostate is commonly referred to as “segmentation”. The oncologist uses the segmented volume to define a treatment plan specifying the locations in the prostate for which the radioactive seeds are to be implanted. The seeds are implanted into the prostate by a needle inserted into the prostate and guided by a needle guiding template. Manual segmentation is time consuming. Automated segmentation also is known. However, a need exists for an improved method for delineating the contours of the tissue in the images.